Merging characters body parts with a different edge loop count
Here is an example of different topology you could use to transition from the octagonal arms to the three fingers. The four selected faces are the ones to pay most attention to.



Although, a triangle island surrounded all by quads won't hurt you once in a while. "All quads" is an ideal, it's not a set-in-stone rule. If the mesh can deform without trouble when animated, you're okay. But yeah, it's good to find quad solutions when possible.

I should also point out this loop of faces that only serves to aid the mesh definition when subdivided. You would probably want to do away with this in a model that is a low-poly game asset or something. I left it in as a buffer. You can take it or leave it.



Blend file to play with: